1. Field of the Invention
The present invention relates generally to implantable medical devices, and more specifically relates to fixation apparatus and techniques for body implantable leads.
2. Description of the Prior Art
The earliest body implantable leads used for cardiac pacing were implanted on the outside surface of the heart. The first fixation means used were sutures wherein the electrode was sutured onto the epicardium. Subsequently, leads were made for epicardial use which had suturing pads which were permanently bonded to the body of the lead. U.S. Pat. No. 3,880,169 issued to Starr et al shows a myocardial electrode having a permanently bonded suturing pad. Characteristic of the suturing pad taught by Starr et al is that it is permanently affixed at a single position on the lead body. This is sufficient and even desirable for myocardial applications since the suturing pad is located in close proximity to the electrode. It is used to hold the electrode at the distal tip of the lead body in place against the myocardial tissue.
The substantial popularity of the transvenous type lead has led to a different type of problem. Since the lead is inserted into a vein at a position quite distant from the heart, the lead body must be secured in place at this remote location. The result is that the suturing sleeve to be used in transvenous applications cannot be located at a fixed distance from the distal end of the lead since the distance from the insertion point in the vein to the final implant position of the distal tip varies substantially from patient to patient and will even vary for a given patient depending upon the exact implant procedure used.
The earliest technique used in suturing transvenous leads was to suture directly across the lead body itself and to the vein or surrounding tissue in the vicinity of the veinectomy. This procedure proved satisfactory for silicone rubber type leads. However, with the advent of urethane leads, it has been found that the lead body may be substantially damaged by sutures applied in direct contact with the insulating sheath. This problem is further compounded by the use of relatively softer conductor coils such as drawn brazed strand.
An attempt to overcome this problem is discussed by Dutcher et al in U.S. Pat. No. 4,266,552. This reference teaches a lead anchoring bobbin which accepts a transvenous pacing lead that is frictionally engaged about two opposed disc-shaped elements. The lead anchoring bobbin is then sutured in place. The normal manner of using this invention is to frictionally engage the body of the transvenous pacing lead in the vicinity of the veinectomy and suture it directly in place to adjacent muscle tissue.
The major problem that has developed with the use of the lead anchoring bobbin is that the device must be secured in place using two hands of the attending physician. Two hands are required because the lead body must actually be wrapped around the lead anchoring bobin. This problem is further complicated when, with the use of a permanent lead introducer, the proximal end of the introducer must normally be occluded with the thumb to prevent air embolisms and to curtail the bleeding that is present. After the permanent lead introducer is removed, the vein itself must be occluded acutely to contain the bleeding.